1. Field of the Invention
The present invention relates to an optical imaging apparatus for obtaining optical image information of a subject portion by scanning with beams from a light source.
2. Description of the Related Art
Recently, an optical imaging apparatus called an OCT (Optical Coherence Tomography) has widely been used. The optical imaging apparatus forms a tomogram of the inside of a subject portion based on information on light which returns from the subject portion by irradiating the subject portion with light having low coherence caused in a light source and then scanning a focus position.
As disclosed in U.S. Pat. No. 6,151,127, Optics Express Vol. 6, No. 7, 136-145 (Optical Society of America, on March, 2000), and Japanese Unexamined Patent Application Publication No. 11-72431 which was applied by the present applicant, the above-mentioned optical imaging apparatus can obtain a three-dimensional tomogram of a subject portion by two-dimensionally scanning the subject portion with an objective optical system for condensing light with low coherence to the subject portion and by scanning it in an optical axis direction.
An optical system of the above-mentioned conventional optical imaging apparatus separates the light with the low coherence generated by the light source into irradiation light and reference light by light separating means, scans (two-dimensionally scans) the subject portion with the separated irradiation light, and condenses the light to the subject portion at a focus point of the objective optical system. Then, reflection light and scattering light of the subject portion from the focus point pass through the same optical path as that of the irradiation light, and return to the light separating means again. In this case, the subject portion in the depth direction is scanned by the scanning operation in the optical direction with the objective optical system.
On the other hand, the reference light separated by the light separating means is reflected by reference light reflecting means, and is returned to the light separating means again. Then, the reference light reflecting means advances and regresses in the optical axis direction so that the length of the optical path of the reflected reference light is almost equal to the lengths of the optical paths of the reflection light and the scattering light from the subject portion.
The reflected reference light and the reflection light and scattering light from the subject portion, having almost the same length of the optical paths interfere each other, and an optical detector as optical detecting means detects these light. An output of the optical detector is demodulated by a demodulator and an interfered optical signal is extracted. The extracted optical signal is converted into a digital signal, is thereafter subjected to signal processing, and image data corresponding to the tomogram is generated. The generated image data is displayed on a monitor as a three-dimensional tomogram of the subject portion.
However, the above-mentioned conventional optical imaging apparatus independently comprises means for advancing and regressing the above-described objective optical system in the optical axis direction and means for advancing and regressing the reference-light reflecting means in the optical axis so that the length of the optical path of instrumentation light matches that of the reference light. Consequently, the above-mentioned conventional optical imaging apparatus has two drive systems.
Thus, the above-mentioned conventional optical imaging apparatus has a larger optical system. When it is incorporated in an endoscope insertion portion or an optical scanning probe which is used by being inserted into the body cavity, there is such a problem that the diameter of these insertion portions becomes large.
Further, the above-mentioned conventional optical imaging apparatus has two control systems for individually controlling the above drive systems. The two drive systems must be controlled synchronously with the two control systems. Therefore, the above-mentioned optical imaging apparatus has complex structures of the control systems and, thus, costs are increased.
The optical imaging apparatus has, for example, an optical probe for scanning the anatomy of the subject portion with laser beams (coherent beams) from the light source and for condensing the light at the focus point of the objective optical system. The optical probe has a conjugate focus-point optical system for obtaining the tomogram of the anatomy by receiving return light, as the reflection light and the scattering light from the anatomy of the subject portion obtained via the objective optical system, by receiving light means having a conjugate focus point of the objective optical system.
As disclosed in, for example, U.S. Pat. No. 5,788,639, the above optical imaging apparatus is proposed, in which the entire optical system is arranged onto a single base and this base is moved in the horizontal direction, thus adjusting a range of a field of view for observation in the horizontal direction. Therefore, in the optical imaging apparatus disclosed in the U.S. Pat. No. 5,788,639, the range of the field of view for observation as a fine observation range is moved in the horizontal direction of the subject portion and the field of view of the objective optical system can be arranged.
On the other hand, as disclosed in, for example, U.S. Pat. No. 5,120,953, an optical imaging apparatus is proposed, in which a surface of the anatomy of a subject portion is absorbed, thereby adjusting the range of the field of view for observation in the vertical direction (depth direction) of the subject portion. Thus, in the optical imaging apparatus disclosed in U.S. Pat. No. 5,120,953, the range of the field of view for observation as a fine observation range can be adjusted in the vertical direction.
As disclosed in Japanese Unexamined Patent Application Publication No. 6-154228 which was applied by the present applicant, an optical imaging apparatus is proposed, in which a TV camera for image pick-up of a surface observation image within the range of the field of view for observation is provided. Consequently, the optical imaging apparatus disclosed in Japanese Unexamined Patent Application Publication No. 6-154228 can simultaneously display both the surface observation image and the tomogram of the subject portion.
Upon moving and adjusting the base on which the entire optical system is arranged, the optical imaging apparatus disclosed in U.S. Pat. No. 5,788,639 requires the adjustment of the optical axis with high accuracy. Thus, in the optical imaging apparatus disclosed in the U.S. Pat. No. 5,788,639, the adjustment of the optical axis is complicated and is difficult.
In the optical imaging apparatus disclosed in U.S. Pat. No. 5,788,639, the base on which the entire optical system is arranged is moved and adjusted. Therefore, the arrangement of the moving and adjusting means in the optical probe causes such a problem that the whole optical probe is increased.
Meanwhile, in the optical imaging apparatus disclosed in U.S. Pat. No. 5,120,953, the range of the field of view for observation can be adjusted in the vertical direction (depth direction) of the subject portion. However, there is such a problem that the range of the field of view for observation cannot be adjusted in the horizontal direction of the subject portion.
Further, in the optical imaging apparatus disclosed in Japanese Unexamined Patent Application Publication No. 6-154228, both the surface observation image and the tomogram of the subject portion can simultaneously be displayed. However, there is such a problem that the range of the field of view for observation cannot be adjusted in the horizontal direction and the vertical direction (depth direction) of the subject portion.
Recently, endoscopes have widely been used in medical fields and industrial fields. As disclosed in Japanese Unexamined Patent Application Publication No. 6-154228, in addition to a normal observation image obtained by the endoscope, an optical tomogram can be obtained with low-coherence light for purpose of the detailed diagnosis about a lesion portion.
In the conventional art, the dimension of the insertion portion in the endoscope can be made thinner because the objective optical system is shared for the normal observation and the optical tomogram using the low-coherence light.
However, in the above-mentioned conventional art, the same numerical aperture (hereinafter, abbreviated to an NA) of the objective optical system is used for both the normal observation and the optical tomogram using the low-coherence light and, therefore, there is a problem to be solved.
More specifically, in the normal usage, first, in a normal observation state, a wide portion is macro-observed. When there is a portion which might be the lesion portion as the observation result, a method is used whereby the case is examined in detail by enlargedly observing a part of the lesion portion with the optical tomogram.
In this case, in the conventional art, the objective optical system is shared and the NA is in the same state. Consequently, in the state suited to the normal observation, a resolution is insufficient for the state of the optical tomogram. On the contrary, in the state of the optical tomogram, the resolution is high by the high NA, a wide field of view cannot be ensured for the normal observation and thus only a narrow range can be observed.
In addition, there is another conventional art using individual optical systems for macro observation and optical tomogram. However, in the endoscope which is inserted in the body cavity as mentioned above, it is difficult to make the diameter of the optical imaging apparatus thinner.
Further, in the case of the other observation art using the individual optical systems, there is such a drawback that the apparatus is increased in size. Moreover, there is such a drawback that when enlarging and observing the lesion portion in the image for macro observation with the optical tomogram, a position to be enlarged and observed with the optical tomogram in the macro image is easily changed in accordance with the change in distance or the like.
It is one object of the present invention to provide an optical imaging apparatus in which an optical system can be reduced in size and a control system can simply be structured.
Also, it is another object of the present invention to provide an optical imaging apparatus with a small size and a high resolution, in which a field of view for observation can easily be moved within a wide range.
Further, it is another object of the present invention to provide an optical imaging apparatus with high convenience, in which both a normal macro image and an enlargedly observed image with a high resolution due to low-coherence light can be obtained by commonly using a part of an optical system so as to arrange the optical imaging apparatus to an endoscope insertion portion.
Furthermore, it is another object of the present invention to provide an optical imaging apparatus used for endoscopes, etc., which is made thinner in diameter and thus can be arranged in an endoscope insertion portion and in which both a normal macro image and an enlargedly observed image with a high resolution due to high-coherence light in an improved convenience state can be obtained.
An optical imaging apparatus comprises: a low-coherence optical system which guides low-coherence light from a low-coherence light source to a subject portion and further guides return light from the subject portion to light receiving means; light separating means arranged to the low-coherence optical system, which separates the low-coherence light from the low-coherence light source into instrumentation light and reference light; horizontal scanning means arranged to the low-coherence optical system, which horizontally scans the subject portion with the instrumentation light separated by the light separating means; reference light reflecting means arranged to the low-coherence optical system, which reflects the reference light separated by the light separating means and returns the reflected light to the light separating means; an objective optical system arranged to the low-coherence optical system, which condenses the instrumentation light horizontally scanned by the horizontal scanning means to the subject portion and further captures return instrumentation-light from the subject portion; optical path length interlockingly adjusting means which interlockingly matches the length of an optical path of the instrumentation light to that of the reference light; and signal processing means which performs signal processing of an electronic signal converted photoelectrically by the light receiving means and obtains a surface image or a tomogram of the subject portion.
An optical imaging apparatus comprises: an optical system which guides beams from a light source to a subject portion and further guides return light from the subject portion to light receiving means; optical scanning means arranged to the optical system, which scans the subject portion with the beams from the light source; an objective optical system arranged to the optical system, which condenses the beams for scanning by the optical scanning means to the subject portion and further captures return light from the subject portion; positioning means arranged in a field of view for observation of the objective optical system, which comes into contact with the subject portion and performs positioning; field of view position adjusting means which moves the positioning means relative to the objective optical system in a contact state of the positioning means with the subject portion and adjusts the position in the field of view of the objective optical system; and signal processing means which performs signal processing of an electronic signal converted photoelectrically by the light receiving means and obtains a surface image or a tomogram of the subject portion.
An optical imaging apparatus comprises: an optical system which guides beams from a light source to a subject portion and further guides return light from the subject portion to light receiving means; a normal optical system in which at least a part thereof is the same as the optical system and which has a numerical aperture smaller than that of the optical system, a focusing distance longer than that of the optical system, an object observation range wider than that of the optical system, or a diameter of the object observation range wider than that of the optical system, and which captures a normal optical image of the subject portion and forming the captured normal optical image by image pickup means; and signal processing means which performs signal processing of an electronic signal photoelectrically converted by the light receiving means, obtains a surface image or a tomogram of the subject portion, performs signal processing the electronic signal converted photoelectrically by the image pick-up means, and obtains a normal optical image.
These objects and advantages of the present invention will become further apparent from the following detailed explanation.